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Carnivora 08-13-2012 01:00 PM

Tips for maximising gas milage in hybrid.
Ok, so I was wondering if any of you Active Hybrid owners have any tips or knowledge about maximizing your milage. I thought I would put my observations down as well.

I have the 10 X6 active hybrid. My old vehicle was a 4.8 X5 08. I was averaging 15 in my X5 based on my driving. With the X6 I'm averaging 19.5. Not bad considering I went up two turbos, 130 hp, and 175 ft. lbs.

So, the first thing I noticed is that it does not benefit, at all, to drive electrically. You don't use any gas, but as soon as the battery is depleted, the engine kicks on and the engine starts charging the batteries, and the mpg goes :thumbdwn:. The only thing that maximises mpg is maximizing what goes into the batteries while braking.

So up until about a month ago, I was driving a completely different style. I was trying to maximize my milage by driving like a grandma at starts and coasting as far as possible in neutral whenever possible. So I was using the electric motor quite a bit, the engine didn't kick in until around 20 mph. This put quite a drain on the battery, and I noticed that sometimes when I stop the battery would hardly charge at all. I would coast in neutral when possible but put it back in gear before slowing down (doesn't charge in neutral). But sometimes when I would stop, the battery would charge quite a bit. I've also seen that the gas milage seems to be the best around 38-39 miles per hour. The problem is that the engine want's to switch off at that speed and you charge and discharge the batteries. It seems as though it causes the batteries to get hot and then when you have to stop, very little energy goes back into the batteries.

So now I'm driving quite different. Off the line, I try to get on the gas and use "electric only" as little as possible. It still uses the electric motors to bump the acceleration but because the engine is doing most the work, less drain on the batteries, which means less "engine charging" the batteries. (I get about 13-14 mpg while "engine charging" at 42mph)

I still coast as much as possible in neutral. In gear, it has quite a bit of engine braking and sometimes I can coast for 5 times as far if I time the lights just right.

I try to drive at least 42 mph to keep the engine from switching off. Really the only charging I want is from braking. Also, at 42, it runs in 7th gear. The faster I get to 7th gear the better. Sometimes if I have to drive less than 42, I put it in sport mode and manually gear it to 6th or 7th depending on the speed.

Got to pick my kid up from school. More later.

Carnivora 08-14-2012 01:45 PM

So now I can average around 20-21. But some things I'm curious about. How much does the air conditioner drain, and is it variable based on temperature or is it an either on or off situation. I'm in mississippi so I run the air 9 months out of the year. Sometimes more to pull the humidity out than to cool it off.

So stop and go traffic kills the milage as well. When I pick my kid up from car rider, you get in line. Then you wait, then you go, then you stop, then you go, then you stop, ad nauseam. It drains the battery and the engine eventually kicks back in, and not only are you "engine charging" again, because you drained that batteries, and are now charging the batteries, they are so hot that the system doesn't charge them as much from braking. Double whammy.

If the engineers really wanted to maximise fuel efficiency, the should decrease the rate of charge while engine charging, or cut out the engine charging completely. The less engine charging, the more braking energy it would recouperate. Now in the winter, when outside temps are 30-40 degrees cooler, it might be different. But too much engine charging heats up the batteries too much. I wouldn't change how quickly the engine kicks in as it seems that off the line is probably the best use of the electric motors as they produce 100% torque at 0 rpm. The engine actually kicks in pretty easy as it is anyway. You really have to feather the throttle to accelerate electric only. However I have noticed that this too can depend on the temp of the batteries as well. Sometimes I've noticed that I can accelerate harder than others while still remaining in electric only. I think that when the batteries heat up, the system limits how much current goes in or out, which is why sometimes the regenerative braking is less effective, or the engine kicks in sooner at low speeds. They should also stop the engine from shutting off when traveling under 40 unless you are decelerating to a stop. Granted I use my cruise whenever possible, and when driving without cruise the engine does not want to cut off so easily.

I think the reason the reason engineers designed it this way, was so they could market a hybrid that can drive electric only up to 37 miles per hour. I think it's more for show than it ever was for really maximizing milage. Though I'm sure that it accomplished exactly what it was designed to do. If you look at the more recent hybrids, they are mild hybrids and pretty much do exactly what i'm outlining here. The electric motors are more for boost than driving electric only, and they are really designed to maximise braking regeneration.

So, having said all that, I do love my X6 hybrid. It's a fun vehicle for a nerd who likes to figure out how to maximise efficiency. I would like BMW to do three things however.
1. Offer a performance accessory: A lithium battery to replace the NiMH battery with either double the capacity or half the weight.
2. Offer a performance accessory: A solar panel replacement for the sunroof which charges the batteries, and cools the car/batteries when it's parked.
3. Start selling the tri-turbo diesel X6M here in the states.

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